Bolgiano et al., U.S. Pat. No. 4,781,987, discloses wear layers comprising polyurethane and an aminoplast. However, such wear layers did not adhere well directly to a polyvinyl chloride (PVC) support surface. In fact, the invention of Bolgiano et al. is a wear layer comprising a first or upper, exposed layer comprising polyol, aminoplast and an acid catalyst which is adhered to a second layer of polyurethane. While the first layer may contain polyurethane, the specific teaching of Bolgiano et al. is to interpose the second layer of polyurethane between the first aminoplast-containing layer and the PVC support surface rather than applying the first layer directly on a PVC support surface. Further, the aminoplast/polyurethane compositions as disclosed by Bolgiano et al. are limited to about 9% to about 10% polyurethane by weight based on polyurethane, aminoplast and epoxy resin. Bolgiano et al. is hereby incorporated by reference.
Conger et al., U.S. Pat. No. 4,059,709, discloses a process of applying a urethane wear layer directly to a resilient PVC floor covering. However, there is no disclosure of the use of a polyurethane/aminoplast wear layer composition.
Further, Conger et al. disclose a solvent based wear layer composition. The use of a solvent not only eliminates the solubility problems of an aqueous system, but it is known in the art that solvents improve adhesion to a vinyl system. The solvent swells the vinyl permitting the wear layer composition to obtain a better "bite".
As indicated by Bolgiano et al., the urethane layer of Conger et al. has certain drawbacks, including being more susceptible to staining. See Bolgiano et al., column 1, lines 32-39. The solution of Bolgiano et al. is to substitute an aminoplast composition for the polyurethane composition of Conger et al. However, as stated by Bolgiano et al. at column 1, lines 54-56, such aminoplast compositions have never been successfully applied to flooring structures, in particular, to vinyl flooring structures. Therefore, Bolgiano et al. teaches that aminoplast compositions including those containing a polyurethane, such as Examples 13 to 18, do not adhere well directly to vinyl flooring structures. Rather, their invention is to dispose a polyurethane layer between the aminoplast/urethane layer and the PVC layer.
Other prior art, such as Moore, U.S. Pat. No. 4,197,392, and Anderson et al., U.S. Pat. No. 4,119,762, suggest aminoplast coatings. However, these do not suggest the use of polyurethane in combination with the aminoplast.
While Chang, U.S. Pat. No. 4,528,344, discloses generically a coating composition of polyurethane and the reaction product of a non-aromatic polyol having a molecular weight of less than 230 and an aminoplast, there are no examples of such a combination. Further, there is no indication of the amount of polyurethane to be included in the composition or the application of such a composition directly to a PVC support surface. In the only example in which the composition is applied to a support surface, Example 8(b), the reaction product is mixed with a pigment, acrylic resin, epoxy resin, xylene and catalyst, and is applied to a zinc phosphate-treated metal panel. The remaining examples merely give examples of the polyol/aminoplast reaction product.
Santer et al., U.S. Pat. No. 4,425,466, discloses a coating composition comprising an aminoplast and a polyfunctional compound including a urethane polyol. There is no suggestion of applying such a coating composition directly to a PVC support surface. In fact, at column 4, lines 67-68, they indicate the use of a coating compositions on oily steel.
As used herein, the terms "polyvinyl chloride", "PVC" and "vinyl" are intended to include homopolymers containing only vinyl chloride units, copolymers consisting of two homopolymers such as vinyl chloride and vinyl acetate, and compositions containing such homopolymers and copolymers.
It is an object of the invention to provide a wear layer having stain resistance superior to polyurethane which wear layer will adhere well directly to a PVC support surface.
A further object is to provide an aqueous-based composition which yields such a wear layer.
Other objects and advantages of the invention will become apparent upon reading the following detailed description.